Abstract

The ratio of the imaginary to the real part of the complex nonlinear refractive index has been measured by two-wave mixing in acridine orange doped fluorophosphate glass, fluorescein doped boric acid glass, and ruby at argon-ion wavelengths. A new and simple two-wave mixing measurement is described in which one of the beams contributing to a stationary interference pattern in the nonlinear absorber is subject to a phase transient. This results in a variation of the energy coupling between the beams from which the phase of the nonlinear index and also the sign of its real and imaginary parts can be determined. A simple theory based on homogeneously broadened absorption agrees with the phase of the nonlinear index in acridine, but not in fluorescein where excited state absorption is determined to be greater than absorption from the ground state. These results are compared with new nondegenerate two-wave mixing measurements in which the contribution from the phase and absorption gratings can be determined independently.¹ Comparison of results from the two approaches enables the contribution of excited state absorption to the two-wave mixing to be qualified.

© 1989 Optical Society of America